Crossing the Pacific Ocean approach to the Panama Canal, the Bridge of the Americas has a clearance of 201 feet -- one of several limiting factors in the size of ships that can travel through the canal. Gene Sloan, USA TODAY

Celebrity Millennium passengers view new locks under construction near the Pacific entrance of the Panama Canal. The locks are part of an expansion project due to be completed in 2015. Gene Sloan, USA TODAY

At 106 feet wide, the Celebrity Millennium just barely fits into the 110-foot-wide Miraflores Locks. Launched in 2000, the ship is a "Panamax" vessel -- that is, it was built to the maximum size allowed in the canal. Gene Sloan, USA TODAY